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RFC 5247, "Extensible Authentication Protocol (EAP) Key Management Framework", August 2008

Source of RFC: eap (int)

Errata ID: 5011

Status: Reported
Type: Technical

Reported By: Jouni Malinen
Date Reported: 2017-05-07

Section Appendix A says:

   EAP-AKA

      EAP-AKA is defined in [RFC4187].  The EAP-AKA Session-Id is the
      concatenation of the EAP Type Code (0x17) with the contents of the
      RAND field from the AT_RAND attribute, followed by the contents of
      the AUTN field in the AT_AUTN attribute:

      Session-Id = 0x17 || RAND || AUTN

It should say:

   EAP-AKA

      EAP-AKA is defined in [RFC4187].  When using full authentication,
      the EAP-AKA Session-Id is the
      concatenation of the EAP Type Code (0x17) with the contents of the
      RAND field from the AT_RAND attribute, followed by the contents of
      the AUTN field in the AT_AUTN attribute:

      Session-Id = 0x17 || RAND || AUTN

      When using fast re-authentication, the EAP-AKA Session-Id is the
      concatenation of the EAP Type Code (0x17) with the contents of the
      NONCE_S field from the AT_NONCE_S attribute, followed by the
      contents of the MAC field from the AT_MAC attribute from
      EAP-Request/AKA-Reauthentication:

      Session-Id = 0x17 || NONCE_S || MAC

Notes:

RFC 5247 was supposed to define exported parameters for existing EAP methods in Appendix A. The way Session-Id was defined for EAP-AKA and EAP-SIM works only for the full authentication case, i.e., it cannot be used when the optional fast re-authentication case is used since the used parameters (RAND, AUTN, NONCE_MT) are not used in the fast re-authentication case. Based on RFC 4187 chapter 5.2 (and similar chapter in RFC 4186), NONCE_S corresponds to RAND and MAC in EAP-Request/AKA-Reauthentication corresponds to AUTN. That would seem to imply that the Session-Id could be defined using NONCE_S and MAC instead of RAND and AUTN/NONCE_MT.

The corrected text in this errata shows the changes for EAP-AKA. Similar changes should be done for EAP-SIM (replace RAND || NONCE_MT with NONCE_S || MAC for fast re-authentication).

It should be noted that EAP-AKA' (RFC 5448) specification did not follow the MUST requirement in RFC 5247, i.e., it did not define Session-Id derivation. That could be done in an update of RFC 5247 with a clone of EAP-AKA design.

In addition, RFC 5247 did not define Session-Id definition for PEAP and there does not seem to exist any IETF RFC which such definition. That could also be included in RFC 5247 update and done similarly to EAP-TLS (Session-Id = EAP type || client.random || server.random).

It would be good to have a clear IETF reference for these details since EAP Session-Id is needed for ERP (RFC 6696) and that is now seeing additional implementation and deployment interest as a component of FILS authentication (IEEE 802.11ai). Same definition of EAP Session-Id is needed to make FILS shared key authentication implementation interoperable.

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